Formula 2 Pf

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2 Formulae

2.1 Using Formulae

In formulae, letters are used to represent numbers. For example, the formula

A l w=

can be used to find the area of a rectangle. HereA is the area, l

the length and w the width. In this formula, l w means l w .

Formulae are usually written in this way without multiplication

signs.

The perimeter of the rectangle would be given by the formula

P l w= +2 2

Here again there are no multiplication signs, and 2 l means 2 l and 2w means 2 w .

Worked Example 1The perimeter of a rectangle can be found using the formula

P l w= +2 2

Find the perimeter if l w= =8 4and .

Solution

The letters l and w should be replaced by the numbers 8 and 4.

This gives

P= +

2 8 2 4= +16 8

= 24

Worked Example 2

The final speed of a car is v and can be calculated using the formula

v u a t = +

where u is the initial speed, a is the acceleration and tis the time taken.

Find v if the acceleration is 2 m s1, the time taken is 10 seconds and the initial speed is 4 m s1.

Solution

The acceleration is 2 m s1 so a = 2 . The initial speed is 4 m s1 so u = 4 .

The time taken is 10 s so t = 10 .

Using the formula

v u a t = +

gives

v = + 4 2 10

= +4 20

=24

1m s

l

w


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Exercises

1. The area of a rectangle is found using the formula A l w= and the perimeter

using P l w= +2 2 . Find the area and perimeter if:

(a) l w= =4 2and (b) l w= =10 3and

(c) l w= =11 2and (d) l w= =5 4and

2. The formula v u a t = + is used to find the final speed.

Find v if`:

(a) u a t= = =6 2 5, and (b) u a t= = =0 4 3, and

(c) u a t= = =3 1 12, and (d) u a t= = =12 2 4, and

3. Use the formula F m a= to find Fif:

(a) m = 10 and a = 3 (b) m = 200 and a = 2

4. The perimeter of a triangle is found using the formula

P a b c= + +

Find P if:

(a) a = 10 , b = 12 and c = 8

(b) a = 3 , b = 4 and c = 5

(c) a = 6 , b = 4 and c = 7

5. The volume of a box is given by the formula

V a b c=

Find Vif:

(a) a = 2 , b = 3 and c = 10

(b) a = 7 , b = 5 and c = 3

(c) a = 4, b = 4 and c = 9

6. Find the value of Q for each formula using the values given.

(a) Q x y= +3 7 (b) Q x y= +2

x y= =4 2and x y= =3 5and

(c) Q x y= + 4 (d) Q x y= 5 2

x y= =3 5and x y= =10 2and

a

b

c

b

ac


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(e) Q x y= 2 (f) Qx

y=

x y= =10 2and x y= =24 2and

(g) Q xy

= + 4 (h) Q xy

= +4 2

x y= =8 3and x y= =5 11and

(i) Q x y z= + +3 2 (j) Q x y y z= +

x y z= = =4 2 10, and x y z= = =2 5 8, and

(k) Q x y z= (l) Q x y z= + 4

x y z= = =2 5 3, and x y z= = =8 3 4, and

(m) Qx y

z=

+(n) Q

x

y z=

+

x y z= = =8 10 3, and x y z= = =50 2 3, and

7. This formula is used to work out Sharon's pay.

Sharon works for 40 hours.

Her rate of pay is 3 per hour.

Pay Number of hours worked Rate of pay= + 10 .

Work out her pay.

(LON)

8. A rectangle has a length ofa cm and a width ofb cm.

The perimeter of a rectangle is given by the formula p a b= +( )2 .

Calculate the perimeter of a rectangle when a b= =4 5 4 2. .and .

(SEG)

2.2 Construct and Use Simple FormulaeAformula describes how one quantity relates to one or more other quantities. For

example, a formula for the area of a rectangle describes how to find the area, given the

length and width of the rectangle.

The perimeter of the rectangle would be given by the formula

P l w= +2 2

Here again there are no multiplication signs and 2 l means 2 l and 2w means 2 w .

Worked Example 1

(a) Write down a formula for the perimeter of the

shape shown.

(b) Find the perimeter if

a b c= = =2 3 5cm, cm and cm

b b

a a

c


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(e) (f)

a = 10 cm a b c= = =4 5 9cm, cm, cm

(g) (h)

a b= =60 160cm, cm, a b= =4 9cm, cm

c = 80 cm

2. Find a formula for the area of each of the shapes below and find the area for the

values given.

(a) (b)

a b= =6 10cm, cm a = 3 cm

(c) (d)

a b= =2 8cm, cm a b c= = =3 4 9cm, cm, cm

(e) (f)

a b= =4 5cm, cm

a b= =50 200cm, cm

a

a

a

a

a

a

aa

b

b

c

c

a a

b b

c

b

a

2a

a

b

a

a

a

b

b

c

a

a

a

b

a

b

b

a

b


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3. Three consecutive numbers are to be added together.

(a) If x is the smallest number, what are the other two?

(b) Write down a formula for the total, T, of the three numbers, using your

answer to (a).

4. (a) Write down a formula to find the mean,M, of the two numbers x and y.

(b) Write down a formula to find the mean,M, of the five numbers p, q, r, s,

and t.

5. Tickets for a school concert are sold at 3 for adults and 2 for children.

(a) If p adults and q children buy tickets, write a formula for the total value, T, of

the ticket sales.

(b) Find the total value of the ticket sales if p = 50 and q = 20 .

6. A rectangle is 3 cm longer than it is wide.

Ifx is the width, write down a formula for:

(a) the perimeter; P;

(b) the area,A, of the rectangle.

7. Rachel is one year older than Ben. Emma is three years younger than Ben

If Ben isx years old, write down expressions for:

(a) Rachel's age;

(b) Emma's age;

(c) the sum of all three children's ages.

8. A window cleaner charges a fee of 3 for visiting a house and 2 for every window

that he cleans.

(a) Write down a formula for finding the total cost Cwhen n windows are

cleaned.

(b) Find Cif n = 8.

9. A taxi driver charges a fee of 1, plus 2 for every mile that the taxi travels.

(a) Find a formula for the cost Cof a journey that covers m miles.

(b) Find Cif m = 3.


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10. A gardener builds paths using paving slabs laid out in a pattern

as shown, with white slabs on each side of a row of red slabs.

(a) If n red slabs are used, how many white

slabs are needed?

(b) Another gardener puts a white slab at each end of the

path as shown below.

Ifn red slabs are used, how many white slabs are needed?

11. A path of widthx is laid around a rectangular lawn as shown.

(a) Find an expression for the perimeter of the grass.

(b) Find an expression for the area of the grass.

12. Choc Bars cost 27 pence each.

Write down a formula for the cost, Cpence, ofn Choc Bars.

(LON)

13. (a) Petrol costs 45 pence per litre.

Write down a formula for the cost, Cpence, ofl litres of petrol.

(b) Petrol costsx pence per litre.Write down a formula for the cost, Cpence, ofl litres of petrol.

(SEG)

14. (a) Vijay earns P in his first year of work.

The following year his salary is increased by Q.

Write down an expression for his salary in his second year.

(b) Julie earns Xin her first year of work.

Her salary is increased by 650 every year.

How much will she earn in

(i) the 5th year (ii) the nth year?

2.3 Revision of Negative NumbersBefore starting the next section on formulae it is useful to revise how to work with negative

numbers.

Note

When multiplying or dividing two numbers, if they have the same sign the result will be

positive, but if they have differentsigns the result will be negative.

20

30grass

path

x


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Worked Example 1

Find

(a) ( ) ( )3 7 (b) ( ) 24 3

(c) ( ) ( )40 5 (d) ( ) 6 7

Solution

(a) ( ) ( ) =3 7 21 (b) ( ) = 24 3 8

(c) ( ) ( ) =40 5 8 (d) ( ) = 6 7 42

Note

When adding or subtracting it can be helpful to use a number

line, remembering to move up when adding and down when

subtracting a positive number. When adding a negative number,

move down and when subtracting a negative number, move up.

Worked Example 2

Find

(a) 4 10 (b) +6 8

(c) 4 5 (d) + ( )6 7

(e) 7 4 ( )

Solution

(a) 4 10 6 = (b) + = +6 8 2

(c) = 4 5 9 (d) + ( ) = 6 7 6 7

= 13

(e) 7 4 7 4 ( ) = +

= 11

Exercises

1. (a) 6 8 = (b) + =8 12 (c) + =5 2

(d) =6 2 (e) ( ) ( ) =8 3 (f) ( ) ( ) =9 6

(g) ( ) ( ) =24 3 (h) 16 2 ( ) = (i) ( ) ( ) =81 3

(j) + =16 24 (k) =8 5 (l) ( ) =5 7

(m) 3 8 ( ) = (n) =1 10 (o) + =10 5

(p) 9 6+ ( ) = (q) 4 7 ( ) = (r) ( ) =1 4

(s) + ( ) =1 7 (t) + ( ) =4 2 (u) ( ) =6 5

4

3

2

1

0

1

2

3

4

Number

line


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2. (a) ( )12

(b) ( )42

(c) ( ) + ( )4 32 2

3. In Carberry, the temperature at midday was 5 C .

At midnight the temperature had fallen by 8 C .

What was the temperature at midnight?

(MEG)

4. The temperature was recorded inside a house and outside a house.

Inside temperature Outside temperature

16 C 8 C

How many degrees warmer was it inside the house than outside?(SEG)

2.4 Substitution into FormulaeThe process of replacing the letters in a formula is known as substitution.

Worked Example 1

The length of a metal rod is l. The length changes with temperature and can be found by

the formulal T= +40 0 02.

where Tis the temperature.

Find the length of the rod when

(a) T = 50 C and (b) T = 10 C

Solution

(a) Using T = 50 gives

l = + 40 50 0 02.

= +40 1

= 41

(b) Using T = 10 gives

l = + ( ) 40 10 0 02.

= + ( )40 0 2.

= 40 0 2.

= 39 8.


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Worked Example 2

The profit made by a salesman when he makes sales on a day is calculated with the

formula

P n= 4 50

Find the profit if he makes

(a) 30 sales (b) 9 sales

Solution

(a) Here n = 30 so the formula gives

P = 4 30 50

= 120 50

= 70

(b) Here n = 9 so the formula gives

P = 4 9 50

= 36 50

= 14

So a loss is made if only 9 sales are made.

Exercises

1. The formula below is used to convert temperatures in degrees Celsius to degreesFahrenheit, where Fis the temperature in degrees Fahrenheit and Cis the

temperature in degrees Celsius.

F C= +1 8 32.

Find Fif:

(a) C = 10 (b) C = 20 (c) C = 10

(d) C = 5 (e) C = 20 (f) C = 15

2. The formula

s u v t = +( )1

2

is used to calculate the distance, s, that an object travels if it starts with a velocity u

and has a velocity v, tseconds later.

Find s if:

(a) u v t= = =2 8 2, , (b) u v t= = =3 5 10, ,

(c) u v t= = =1 2 3 8 4 5. , . , . (d) u v t= = =4 8 2, ,

(e) u v t= = =4 8 5, , (f) u v t= = =1 6 2 8 3 2. , . , .


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3. The length, l, of a spring is given by the formula

l F= 20 0 08.

where Fis the size of the force applied to the spring to compress it.

Find l if:

(a) F = 5 (b) F = 20

(c) F = 24 (d) F = 15

4. The formula

P n= 120 400

gives the profit, P, made when n cars are sold in a day at a showroom.

Find P if:

(a) n = 1 (b) n = 3

(c) n = 4 (d) n = 10

How many cars must be sold to make a profit?

5. Work out the value of each function by substituting the values given, withoutusing

a calculator.

(a) V p q= +2 2 (b) p a b= 2 2

p q= =8 4and a b= =10 and 7

(c) z x y= + (d) Q x y=

x y= =10 and 6 x y= =15 6and

(e) Px y

=+

2(f) Q

a

b=

x y= = 4 10and a b= =100 4and

(g) Vx y z

=+ +2

5(h) R

a b= +

1 1

x y z= = =2 5 8, and a b= =4 2and

(i) Sa

b

b

c= + (j) R a b= +0 2 0 4. .

a b c= = =3 4 16, and a b= =10 20and

(k) Ta b

= +2 5

(l) Ca b

a b=

+

a b= =20 40and a b= = 10 5and

(m) Px

y= 2

2

(n) Aa b

c=

2

x y= =10 4and a b c= = =2 3 100, and


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(o) Xb c

a=

+(p) z x y= +

2 2

a b c= = =10 1 7 2 1, . .and x y= =3 4and

(q) P a b= 2 2 (r) Q x y z= + +2 2 2

a b= =10 6and x y z= = =10 5 10, and

6. Work out the value of each function by substituting the values given, using a

calculator if necessary.

(a) Px y

z=

(b) V

x y

x y=

+

x y= =10 2 02, . x y= =4 9 3 1. .and

and z = 2 1.

(c) Rx y

=

2 2

4(d) D

x y= +

2 2

x y= =3 6 1 6. .and x y= =0 4 0 8. .and

(e) Qx y

=+

2 2

5(f) V

x y

x y=

+

+

3 2

x y= =3 7 5 9. .and x y= =1 6 2 4. .and

(g) R p qp q

= +

(h) A x y

x y= +

+

2 2

p q= = 1 2 0 4. .and x y= = 5 2 1 2. .and

(i) P xy

= 10

x y= = 3 09 106. and

7. The formula to convert temperatures from degrees Fahrenheit ( F ) into degrees

Celsius ( C) is

C F= ( )5

932

Calculate the temperature in degrees Celsius which is equivalent to a temperature

of 7 F .

(MEG)

8. FR

= +9

432

Calculate the value ofFwhen R = 20 .

(LON)


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Solution

Substituting these values into the formula gives

z2 2 23 6 4 8= +. .

z2 12 96 23 04= +. .

z2 36=

Now the square root can be taken of both sides to give

z = + 36 36or

z = 6 6or

Exercises

1. Use the formula

1 1 1

f v u= +

to findfif:

(a) v u= =3 4and (b) v u= = 6 5and

(c) v u= = 7 3and (d) v u= = 10 4and

2. Findz using the formula

z x y2 2 2= +

if:

(a) x y= =1 2 0 5. .and (b) x y= =4 8 6 4. .and

(c) x y= =3 1 6and .

3. Find the value of z as a fraction or mixed number in each case below.

(a)1

z

x

x y=

+(b)

1

z

x

y

y

x= +

x y= = 4 10and x y= =3 4and

(c)1 2 3

z x y= + (d)

1

z

x y

x y=

+

x y= = 4 5and x y= = 7 3and

(e)1

4

3

z

x

y= + (f)

1 1

1z

x

x=

+

x y= = 5 2and x = 2


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(g)1 2

4z

x

x=

+(h)

x y

x y z

+

=

1

x =1

4x y= =4

1

2and

(i)x

y z2

3 1+ =

x y= =1 6and

4. Findz in each case below.

(a) z x2 2

9= + (b) z x y2

= +

x = 4 x y= = 147 3and

(c) z x y2

= (d) zx

y2 =

x y= = 44 5and x y= =363 3and

(e) zx

y

2 6=

+(f) z

x

y

2

8=

+

x y= =6 3and x y= = 16 9 7 9. .and

5. When three resistors are connected in parallel the total resistanceR is given by

1 1 1 1R X Y Z

= + +

whereX, YandZare the resistances of each resistor.

FindR if:

(a) X Y Z= = =10 20 30, and

(b) X Y Z= = =1000 5000 2000, and

(c) X Y Z= = =1500 2200 1600, and

6. Use the formula

yx

t v=

( )

1

2

to calculate the value ofy given that

x t v= = =50 2 5 0 6, . .and

Give your answer correct to 1 decimal place.

Show all necessary working.

(LON)


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7. The formula fu v

u v=

+is used in the study of light.

(a) Calculate f when u v= = 14 9 10 2. .and .

Give your answer correct to 3 significant figures.

(b) By rounding the values ofu and v in part (a) to 2 significant figures,

check whether your answer to part (a) is reasonable.

Show your working.

(MEG)

8. A ball bearing has mass 0.44 pounds.

1 2 2kg pounds= . .

(a) (i) Calculate the mass of the ball bearing in kilograms.

Densitymass

volume=

(ii) When the mass of the ball bearing is measured in kg and the

volume is measured in cm3, what are the units of the density?

(b) The volume of a container is given by the formula

V L L= ( )4 32

Using Mass = Volume Density calculate the mass of the

container when L = 1.40 cm , and 1 cm3 of the material has a mass

of 0.160 kg.

2.6 Changing the SubjectSometimes a formula can be rearranged into a more useful format. For example, the

formula

F C= +1 8 32.

can be used to convert temperatures in degrees Celsius to degrees Fahrenheit. It can be

rearranged into the form

C=

. . .to enable temperatures in degrees Fahrenheit to be converted to degrees Celsius. We say

that the formula has been rearranged to make Cthe subject of the formula.

Worked Example 1

Rearrange the formula

F C= +1 8 32.

to make Cthe subject of the formula.


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Solution

The aim is to remove all terms from the right hand side of the equation except for the C.

First subtract 32 from both sides, which gives

F C =32 1 8.

Then dividing both sides by 1.8 gives

FC

=

32

1 8.

So the formula can be rearranged as

CF

= 32

1 8.

Worked Example 2

Make v the subject of the formula

su v t

=+( )2

Solution

First multiply both sides of the formula by 2 to give

2s u v t = +( )

Then divide both sides by t, to give

2st

u v= +

Finally, subtract u from both sides to give

2s

tu v =

So the formula becomes

vs

tu=

2

Exercises

1. Makex the subject of each of the following formulae.

(a) y x= 4 (b) y x= +2 3 (c) y x= 4 8

(d) yx

=+ 2

4(e) y

x=

2

5(f) y x a= +

(g) yx b

a=

(h) y a x c= + (i) y

a x b

c=

+

(j) ya x c

b=

(k) y a b x= + + (l) y

x a b

c=

+


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(m) y a b x= (n) y a b x c= + (o) ya x b

c=

4

3

(p) pa x b c

d=

(q) y a x b= +( ) (r) y

x a=

+( )3

4

(s) qx

=( )3 4

2(t) v

x y=

+( )5

4(u) z a

x= +

( )3

4

2. Ohm's law is used in electrical circuits and states that

V I R=

Write formulae withIandR as their subjects.

3. Newton's Second law states that F m a= .

Write formulae with m and a as their subjects.

4. The formula C r= 2 can be used to find the circumference of a circle.

Make rthe subject of this formula.

5. The equation v u a t = + is used to find the velocities of objects.

(a) Make tthe subject of this formula.

(b) Make a the subject of this formula.

6. The mean of three numbersx, y and z can be found using the formula

mx y z

=+ +

3

Makez the subject of this formula.

7. Make a the subject of the following formulae.

(a) v u a s2 2 2= + (b) s a t a t = +1

2

2

8. The formula V x y z= can be used to find the volume of a rectangular box.

Makez the subject of this formula.

9. The volume of a tin can is given by

V r h= 2

where ris the radius of the base and h is the height of the can.

(a) Make rthe subject of the equation.

(b) Find rcorrect to 2 decimal places if V h= =250 10cm and cm3 .


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10. A box with a square base has its volume given by

V x h=2

and its surface area given by

A x x h= +2 42

(a) Make h the subject of both formulae.

(b) Find h if A x= =24 22cm and cm .

(c) Find h if V x= =250 103cm and cm .

11. The area of a trapezium is given by

A a b h= +( )1

2(a) Write the formula with a as its subject.

(b) In a particular trapezium b a= 2 .

Use this to write a formula that does not

involve b, and make a the subject.

2.7 Further Change of SubjectThis section uses some further approaches to rearranging formulae.

Worked Example 1

Make l the subject of the formula

Tl

g= 2

Solution

First divide both sides by 2 to give

T lg2

=

Now the square root can be easily removed by squaring both sides of the equation, to give

T l

g

2

24

=

Finally, both sides can be multiplied by g to give

T gl

2

24

=

h

x

x

a

b

h


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so the rearranged formula is

lT g

=

2

24

Worked Example 2Makex the subject of the formula

y x= 6 5

Solution

To avoid leaving 5x on the right hand side of the formula, first add 5x to both sides

to give

y x+ =5 6

Then subtract y from both sides to give

5 6x y=

Finally, divide by 5 to give

xy

=6

5

Worked Example 3

Makex the subject of the formula

qx y

= +1 1

Solution

First subtract1

yfrom both sides so that the right hand side contains only terms

involvingx.

qy x

=1 1

Now combine the two terms on the left hand side of the formula into a single fraction, by

first makingy the common denominator.

q yy y x

=1 1

q y

y x

=

1 1

Now both fractions can be turned upside-down to give

x y

q y1 1=

or

x

y

q y=

1


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Exercises

1. Rearrange each of the following formulae so thatx is the subject.

(a) y x=

5 3 (b) y x=

8 6 (c) y a x=

2

(d) yx

=6 2

5(e) y

x=

8 7

2(f) y

x=

7 5

3

(g) pa x b

=

2(h) q

x

a=

+8 2(i) r

q x

b=

5

2. For each formula below make a the subject.

(a) qa

=

4

(b) za

b

= (c) zc

a

=

(d) ya

= 22

3(e) v

a

b=

1

4 2(f) r

a= 5

(g) pa b

=+

4(h) r

b a=

1

2 3(i) c

b a=

+3

2

3. Make u the subject of each of the following formulae.

(a) a u= +1 1

2 (b) b u= 1

2 (c) x u= 21

(d)1 1 1

3x u= + (e)

1 1 1

5p u= (f)

1 2 1

3x u= +

(g)1 4 2

r u v= + (h)

1 1

7

1

q u= (i)

1 1 1

p a u=

4. The formula Tl

g= 2 gives the time for a pendulum to complete one full

swing.(a) Make g the subject of the formula.

(b) Find g if l T= =0 5 1 4. .and .

5. The formula1 1 1

f u v= + is used to find the focal length of a lens.

(a) Make v the subject of the formula.

(b) Find v if f u= =12 8and .


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6. If a ball is dropped from a height, h, it hits the ground with speed, v, given by

v g h= 2

(a) Make h the subject of this formula.

(b) Find h if g v= =10 6and .

(c) Make g the subject of the formula.

(d) Find the value ofg on a planet when h v= =10 4, .

7. A ball is thrown so that it initially travels at 45 to the horizontal. If it travels a

distanceR, then its initial speed, u, is given by

u g R=

(a) MakeR the subject of the formula.

(b) FindR if u g= =12 10and .

8. When three resistors with resistancesX, YandZare connected

as shown in the diagram, the total resistance is R, and

1 1 1 1

R X Y Z= + +

(a) MakeXthe subject of this equation.

(b) FindXif R Y Z= = =10 30 40, and .

9. The volume of a sphere is given by the formula V r=4

3

3 .

(a) Rearrange the formula to give r, in terms ofV.

(b) Find the value ofrwhen V = 75.

(SEG)

2.8 Expansion of Brackets

An equation or formula may involve brackets as, for example, in st

u v= +( )2

.

Removing the brackets from such an expression is a process known as expanding.

Worked Example 1

Expand 4 8x +( ).

Solution

Each term inside the bracket must be multiplied by the 4 that is in front of the bracket.

4 8 4 4 8x x+( ) = +

= +4 32x

X Y Z


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Worked Example 2

Expand x x ( )2 .

Solution

Every item in the bracket must be multiplied byx. This gives

x x x x x( ) = + ( )2 2

= x x2 2

Worked Example 3

Expand ( )2 4 3x .

Solution

Each term inside the bracket is this time multiplied by 2 .

( ) = + ( ) ( )2 4 3 2 4 2 3x x

= +8 6x

Worked Example 4

Expand and simplify x x x( ) + +( )2 4 2 1 .

Solution

Each bracket must be expanded first and then like terms collected.

x x x x x x x( ) + +( ) = + + 2 4 2 1 2 4 2 4 1

= + +x x x2

2 8 4

= + +x x2

6 4

Exercises

1. Expand the following:

(a) 3 1x+

( ) (b) 4 2a+

( ) (c) 3 6x

( )(d) 5 3 ( )b (e) 2 8 ( )x (f) 3 4x +( )

(g) 2 5 12x ( ) (h) 6 2 5x ( ) (i) 3 2 7x +( )


(a) +( )2 6x (b) +( )3 2x (c) ( )6 3x

(d) ( )7 2x (e) +( )4 2 1x (f) ( )5 3 2x

(g) ( )2 3 8x (h) ( )3 4 x (i) ( )8 2 4x


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(a) x x +( )1 (b) x x1 ( ) (c) x x ( )6

(d) ( )x x3 2 (e) ( )x x4 6 (f) a a4 5+( )

(g) 3 2 5a a ( ) (h) 3 4 21y y ( ) (i) 6 5 2y y( )

4. Expand and simplify the following:

(a) 3 2 8+ ( )x (b) x x x+( ) 1 3

(c) 5 7 12x +( ) (d) 4 2 2 1x x+( ) + ( )

(e) 3 6 2 4 5x x( ) + ( ) (f) 4 2 6n n n( ) + +( )

(g) 4 6 2 2a a+( ) ( ) (h) 3 2 4 6x x x( ) ( )

(i) 2 1 7x x x x+( ) ( )

5. Remove the brackets from each expression and simplify if possible.

(a) x x2

1+( ) (b) 2 52x x x( )

(c)1

24 12x +( ) (d)

2

312 6x ( )

(e) 3 2 42x x ( ) (f) x x x x2 24 3 2+( ) + +( )

(g) a p q p a b+( ) + +( ) (h) 3 4 2n x y x y n+( ) + ( )

(i) x p q p x q q p x+( ) + +( ) ( )

6. Find the area of each rectangle below.

(a) (b) (c)

7. In a game, Stuart asks his friend to think of a number, add 1 to it and then double

the result.

(a) using x to represent the unknown number, write Stuart's instructions, using

brackets.

(b) Expand your answer to (a).

(c) Describe an alternative set of instructions that Stuart could use.

(d) Repeat (a) to (c) for an alternative game where Stuart asks his friend to thinkof a number, add 1 to it and then multiply the result by the number first

thought of.

a 1

ax

x + 4

x 2

x


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8.

(a) For the rectangle shown in the diagram, find the length BC.

(b) Find the length AB.

(c) Write an expression involving brackets for the area of the rectangle.

(d) Expand your answer to (c) to give an alternative expression.

2.9 FactorisationThe process of removing brackets is known as expanding. The reverse process of

inserting brackets is known asfactorising. To factorise an expression it is necessary to

identify numbers or variables that are factors of all the terms.

Worked Example 1Factorise

6 8x +

Solution

Both terms can be divided by 2, so it is factorised as:

6 8 2 3 2 4

2 3 4

x x

x

+ = +

= +( )

Worked Example 2Factorise

12 16a

Solution

Here the largest number that both terms can be divided by is 4.

12 16 4 3 4 4

4 3 4

a a

a

=

= ( )

(a, b) (c, b)

(a, O) (c, O)

A

D

B

C

y

xO


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Worked Example 3

Factorise

4 82x x

Solution

Here 4 is the largest number that will divide into both terms but each term can also be divided

byx, so 4x should be placed in front of the bracket.

4 8 4 4 2

4 2

2x x x x x

x x

=

= ( )

Exercises

1. Complete a copy of each of the following.

(a) 5 10 2x x+ = +( )? (b) 6 8 3 4x x = ( )?

(c) 15 25 3 5x x+ = +( )? (d) 12 8 4x + = +( )? ?

(e) 18 6 6 = ( )n ? ? (f) 6 21 3x = ( )? ?

(g) 16 24 8a + = +( )? ? (h) 33 9 3x = ( )? ?

2. Factorise each of the following expressions.

(a) 6 24x + (b) 5 20x (c) 16 8 x

(d) 8 12n + (e) 12 14x (f) 3 24a

(g) 11 66x (h) 10 25+ x (i) 100 40x

(j) 50 40 x (k) 6 30x (l) 5 45y

(m) 12 36+ x (n) 16 32x + (o) 27 33x

3. Complete a copy of each of the following.

(a) x x x2

1+ = +( )? (b) x x x2 2 2+ = +( )?

(c) 2 5 2 52a a a = ( )? (d) 4 2x x x+ = +( )? ?

(e) x x x2

4+ = +( )? ? (f) 6 3 32x x x+ = +( )? ?

(g) x a x b x+ = +( )? ? (h) 4 2 22x a x x = ( )? ?


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(a) 52x x+ (b) a a

23+ (c) 5 2

2n n+

(d) 6 32n n+ (e) 5 10

2n n (f) 3 62x x+

(g) 15 302x x (h) 14 212x x+ (i) 16 242x x+

(j) 30 182x x (k) 5 52

+ n (l) 10 152n

(m) 3 93n n+ (n) 9 27

2x x (o) 10 53 2x x


(a) a x ax+ 2 (b) b x c x+2

(c) 2 4pq rq

(d) 15 5 2x y y (e) 16 24 2pq p+ (f) 6 182x x y+

(g) 3 92p px (h) 24 56 2px x+ (i) 16 182 2x y x y

6. For each factorisation shown below, state if it can be factorised further. If the answer

is yes, give the complete factorisation.

(a) 6 4 2 3 22 2x x x x+ = +( ) (b) 16 8 8 23 2 2x x x x x+ = +( )

(c) 5 60 5 122x x x x = ( ) (d) 3 18 3 62 2 2x y x y x x y y = ( )

7. (a) Factorise completely 36 6 2x x+ .

(b) Given that y x= +3 5

expressx in terms ofy.

2.10 Algebraic ManipulationSometimes a letter may appear twice in a formula, for example,

pw

x w=

+

This section is concerned with how to make the repeated letter the subject of the equation.

Worked Example 1

Make x the subject of the formula

ax c x b = +3

Solution

First bring all the terms containingx to one side of the equation. Subtracting 3x gives

ax x c b =3

Then adding c to both sides gives

ax x b c = +3


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Factorising gives

x a b c( ) = +3

Finally, dividing by a ( )3 gives

xb c

a=

+

3

Worked Example 2

Make w the subject of the formula

pw

x w=

2

Solution

First multiply both sides by x w and expand the brackets.

pw

x w=

2

p x w w

px pw w

( ) =

=

2

2

Next take all the terms containing w to one side of the equation and factorise.

px w pw

px w p

= +

= +( )

2

2

Finally, dividing by 2 +( )p givespx

pw

2 +=

or

wpx

p=

+2

Exercises


(a) 2x a x b+ = (b) a x b c x d =

(c) xa b x = 4 5 (d) 3 6 4 2x a x = +

(e) b x c x = 2 5 (f) a b x c d x =

(g) 2 1x a x+( ) = (h) 4 3x a a x( ) = ( )

(i) p x q x+( ) = ( )1 1 (j)x a x b

=+

2 3

(k)2

51

x ax

= + (l)

x

a

x b=

+

4


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(a) Px

x=

+ 1(b) P

a x b

x=

+(c) Q

x b

x a=

+

(d) qx y

x y

2

=

+

(e)

x

x a

+ =

2

3 (f)

x b

x c

= 4

(g) px

x=

+ 1(h) w

x

x=

2(i) w

x

x=

+

2

1

(j) px

x=

+2

2

2(k) p

x

x=

2

3

2

2(l) g

x y

x y=

+

2

2

2.11 Algebraic Fractions

When fractions are added or subtracted, a common denominator must be used as shown

below:

1

2

1

3

3

6

2

6

5

6

+ = +

=

When working with algebraic fractions a similar approach must be used.

Worked Example 1

Express

x x

6 5+

as a single fraction.

Solution

These fractions should be added by using a common denominator of 30.

x x x x

x

6 5

5

30

6

30

11

30

+ = +

=

Worked Example 2

Express

3 4

1x x+

+



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Solution

In this case, the common denominator will be x x +( )1 .Using this gives

3 4

1

3 1

1

4

1

3 1

1

4

1

7 1

1

x x

x

x x

x

x x

x

x x

x

x x

x

x x

+

+

=+( )+( )

+

+( )

=+

+( )+

+( )

=+

+( )

Worked Example 3Express

3

2 1 1

x

x

x

x++

+


Solution

In this case, the common denominator will be 2 1 1x x+( ) +( ) .Using this gives

3

2 1 1

3 1

2 1 1

2 1

2 1 1

3 3

2 1 1

2

2 1 1

5 4

2 1 1

2 2

2

x

x

x

x

x x

x x

x x

x x

x x

x x

x x

x x

x x

x x

++

+=

+( )+( ) +( )

++( )

+( ) +( )

=+

+( ) +( )+

+

+( ) +( )

=+

+( ) +( )

Exercises1. Simplify each expression into a single fraction.

(a)x x

4 5+ = ? (b)

x x

7 4+ = ? (c)

x x

3 5+ = ?

(d)2

7

5

3

y y+ = ? (e)

2

5

3

4

y y+ = ? (f)

5

7

8

7

y y+ = ?

(g)4

7

3

10

x x = ? (h)

5

6

2

3

x x = ? (i)

x x

4

7

8+ = ?


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(j)5

6

7

24

x x+ = ? (k)

a b

4 5+ = ? (l)

x y

3 8+ = ?

(m)a b

3 5

= ? (n)2

3

4

5

a b+ = ? (o)

8

9

3

4

a b = ?

2. Express the following as single fractions.

(a)4 2

x y+ = ? (b)

6 1

x y = ? (c)

1 3

x y+ = ?

(d)8 3

a a = ? (e)

4 3

2a b+ = ? (f)

5

3

1

2a b = ?

(g)5

3

4

5a b+ = ? (h)

7

3

4

5a a = ? (i)

6

7

1

4a a = ?

(j)7

8

2

3a b = ? (k)

3

6

5

12a a = ? (l)

7

4

3

8a a = ?

3. Combine the fractions below into a single fraction.

(a)1 1

1x x+

+= ? (b)

2 1

2x x+

+= ? (c)

4

1

3

x x++ = ?

(d)5 1

2x x

+= ? (e)

5

2

1

x x = ? (f)

6

3

4

3x x+ = ?

(g)6

1

6

x x+ = ? (h)

4

5

2

x x+ = ? (i)

7

5

4

6x x+

+= ?

(j)5

7

7

2x x+ = ? (k)

6

10

5

3x x+ = ? (l)

1

3

2

8x x+

= ?

4. Simplify each expression below, giving your answer as a single fraction.

(a)1

1

1

2x x++

+= ? (b)

1

1

1

1x x+

+= ?

(c)3

2

4

2x x++

+= ? (d)

4

2

2

6x x+

= ?

(e)1

3

2

4x x+

+= ? (f)

3

7

2

7x x

+= ?

(g)5

4

3

8x x

++

= ? (h)2

4

4

7x x

+

= ?


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(i)3

6

5

1x x++

= ? (j)

1

2 6

1

3 8x x++

= ?

(k)1

2 5

1

5 4x x+

= ? (l)3

2 1

4

3 1x x

+

= ?

(m)5

2 3

6

5 1x x++

= ? (n)

6

3 7

2

2 3x x+

+= ?

(o)7

5 4

3

2 3x x+

+= ?

5. Simplify each expression.

(a)

x

x

x

x+ + =1

2

2 ? (b)

x

x

x

x + =7

2

2 1 ?

(c)x

x

x

x+

=

1

2

3 1? (d)

x

x x++

=

3

4

1?

(e)5

3

3

4

x

x

x

x+

+= ? (f)

x

x

x

x2

4

4 3+

= ?

(g)2

5

3

1

x

x

x

x

+= ? (h)

x

x

x

x4

5

6+

+= ?

(i) xx x+

=6

31

?

Formula 2 Pf

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